Add dark/light theme toggle with styles

Author: MDJAVEED7

css/theme-dark.css

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+/* theme-dark.css */
+
+body {
+    background-color: #121212;
+    color: #f1f1f1;
+}
+
+a {
+    color: #90caf9;
+}
+
+.navbar {
+    background-color: #1f1f1f;
+}
+
+#tg-sb-sidebar {
+    background-color: #1e1e1e;
+    border-right: 1px solid #333;
+}
+
+#tg-sb-content {
+    background-color: #1a1a1a;
+}
+
+pre, code {
+    background-color: #2c2c2c;
+    color: #e0e0e0;
+}

css/theme-light.css

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+/* theme-light.css */
+
+body {
+    background-color: #ffffff;
+    color: #000000;
+}
+
+a {
+    color: #1a0dab;
+}
+
+.navbar {
+    background-color: #f8f9fa;
+}
+
+#tg-sb-sidebar {
+    background-color: #f1f1f1;
+    border-right: 1px solid #ccc;
+}
+
+#tg-sb-content {
+    background-color: #ffffff;
+}
+
+pre, code {
+    background-color: #f5f5f5;
+    color: #333333;
+}